A fiber optic connector requires a high-quality, optical-grade endface surface to maximize coupling efficiency and ensure proper operation of the fiber. Generally, a fiber endface has a desirable geometry or topography, such as a desirable radius of curvature, apex offset, fiber height and angle. The fiber endface also has an acceptable surface quality. Examples of surface defects include scratches, digs and other contaminants. A desirable surface geometry and acceptable surface quality can be achieved through an optical polishing process and tested using two different instruments or two separate processes within a single instrument.
The surface quality of the fiber can be measured using an optical microscope to magnify any scratches, digs, or small irregularities that might be present on the fiber surface. The microscope can be either visual or it can utilize an area array detector (e.g. camera) to generate a digital image. If the microscope is visual, then an operator makes a subjective surface quality judgment by considering the approximate size and shape of the scratches present within a predefined area of the fiber endface. If an area array detector is used, two-dimensional image processing algorithms can extract defects.
The geometry of a fiber endface can be measured with an interferometric device which uses various optical interference techniques to generate a three-dimensional map of the fiber endface. Interferometers effectively generate images of a surface being tested. However, these images are superimposed with optical fringe patterns that obscure large areas of the sample and cannot, therefore, be used to visually search for defects. Therefore, it can be necessary to use a separate optical instrument or separate process in an imaging system to complete the microscope inspection portion of the test and identify small defects.